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90

The Gossamer Albatross is a human-powered plane with a top speed of 29 km/h (18mph). It was used to cross the English Channel and seems to meet the criteria of the question.


81

Because wings work on air moving past them, not ground moving below them. Heck, in a 35 knot headwind, the Antonov-2 could be rolling backwards at 2 knots and still take off!


64

I'd like to answer this question by debunking the premise of the question: that most plane crashes happen when planes fall out of the sky, and that it's like rock climbing where the higher you are, the more likely a fall will kill you. While it sounds believable, it's almost entirely false, and since it isn't diving out of the sky that kills you, lowering ...


61

The Antonov AN-2 has no stall speed quoted in the operating manual and can fly under full control at about 30 mph. Thus if the headwind is sufficiently large the aircraft will move backwards with respect to the ground.


61

It would likely create a more deadly situation. In aviation altitude is your friend. Generally speaking altitude in the case of an emergency buys you time to work the problem. Generally you want to be as high as practical for the aircraft in question. Altitude also buys you glide distance to find a suitable landing location in an emergency. Airplanes ...


55

This is because what you are looking at is the IAS indicator (Indicated Air Speed). This represents the amount of relative air which flows over and under the wings of the plane. This is what creates lift and enables the plane to fly. This is why this instrument is so important and belongs to the primary flight instruments. This is not to be confused with GS ...


45

The Harrier, Yak-38, Yak-141, XV-15, and V-22 are all fixed wing aircraft. All can hover in mid air, controlled. So they are in controlled flight at 0 velocity. At least the Harrier can even be in controlled flight flying backwards, so with negative velocity. The others may as well, I don't know.


44

The speed indicator in the cockpit shows indicated airspeed. Indicated airspeed is usually different than GPS speed, due to wind and aerodynamic effects. GPS speed is your speed with respect to the ground. If you are standing on terra firma it reads 0. If it reads 100 knots you will be 100NM away from where you are now in one hour, so long as you keep ...


43

It is not a unit. It is just Microsoft trying to be funny. Or to convey an idea of the magnitude. Thanks @Jackie for pointing out that around March 2019, Microsoft has released this calculator as open source under MIT license. It is available in this Github repository. The source code sheds light on the definition of these pseudo units: Description in ./...


43

Because what determines the amount of lift generated is the indicated airspeed, not the ground speed. As usual, it is always easier to think about an extreme case. If you have an aircraft with VR (speed at rotation for takeoff) of 90 knots, and there is an 80 knots head wind, in theory it will rotate with ground speed of 10 knots even though the indicated ...


40

You can, but you have to live with the consequences. There are several things that can happen: Depending on the vertical gusts ahead, you might not even get close to v$_{NE}$. There is another speed limit for gusty weather called v$_B$, and exceeding this will run the risk of overstressing the wing structure. Going above v$_B$ will overstress the wings in a ...


38

An airplane can slow down and reduce its speed while in flight. The easiest way to do so is to reduce the amount of thrust that the engines are producing. This will produce an almost immediate reduction of the airspeed, especially if the plane is maintaining the same altitude. There are also devices called air brakes and spoilers that can be further used ...


33

A propeller accelerates the air of density $\rho$ which is flowing through the propeller disc of diameter $d_P$. This can be idealized as a stream tube going through the propeller disc: The air speed ahead is $v_0 = v_{\infty}$ and the air speed aft of the propeller is $v_1 = v_0 + \Delta v$. The propeller effects a pressure change which sucks in the air ...


32

No because aircraft are categorized by their speed at the runway threshold (1.3 times stall speed). VAT —Speed at threshold used by ICAO (1.3 times stall speed in the landing configuration at maximum certificated landing mass) By knowing the category, ATC is able to use appropriate speeds. The category is not actually listed anywhere, so the controller ...


31

At the critical mach number, some part of the aircraft (usually the wing) will have air flowing over it at a speed in excess of mach 1. If the aircraft is not meant to fly at transonic or supersonic speeds, shock waves will flow over the wing. This can either cause the wing to stall, the control surfaces to become unresponsive, or the plane to go into the ...


31

It's an illusion that the blades appear to be going slowly. It's actually a well known effect called the wagon wheel effect. Essentially the rotor is spinning at close to an even multiple of the camera's framerate divided by the number of rotors. This means that between frames the blades have moved a full quarter rotation (or a multiple of that). Creating ...


30

Spoilers have many uses, but first I want to distinguish types of spoilers. Airplanes will typically have ground spoilers and flight spoilers and they work like they sound. Ground spoilers only open up on the ground -- these are usually much more detrimental to lift than the flight spoilers. Flight spoilers open when actuated by the pilots Another type of ...


28

No, it could not fly much faster with the available energy. Lift is a question of wing area and dynamic pressure. Solar Impulse 2 has 269.5 m² wing area to carry its 2.3 tons of mass. This is a wing loading of just 8.53 kg/m²; much less than even gliders have (they start at around 30 kg/m²). This allows it to fly very slowly; if we assume it ...


28

Your airspeed does not remain constant because of inertia: it takes more time for the airplane to adapt to the new relative wind, compared to the time it takes for the wind to change. Example One: you're flying 80 knots and the headwind is 20 knots. Over a time of 3 minutes, the headwind gradually reduces from 20 knots to 10 knots. Since the change is ...


28

To reduce damage in case of a bird strike. The restriction is not only for the 737-100 and -200 models, the 737 NG QRH says: WINDOW HEAT OFF In flight: WINDOWS HEAT switch (affected window) ..... OFF Limit airspeed to 250 knots maximum below 10,000 feet. Pull both WINDSHIELD AIR controls. This vents conditioned air to the inside of ...


25

This answer is written for air transport category aircraft. Introduction During take-off there are three operationally significant speeds that ensure a safe take-off: V1 - the take-off decision speed VR - the rotation speed V2 - the take-off safety speed In addition there are three technically important speeds: VMU the minimum unstick speed VMCG the ...


24

It is not only the mass that affects the landing speed. Wing area plays an important role as well. A larger wing can lift more weight at the same speed than a smaller wing. If you compare the wing loading of these aircraft the differences are smaller: A388: Maximum landing weight: 391000 kg Wing area: 845 m2 Wing loading: 463 kg/m2 B744: Maximum ...


24

Speed of a plane is actually measured in a number of different ways, and relative to different things. Here is a summary of the different types: Indicated Airspeed (IAS). This is the number shown on the instrument that measures airspeed, and isn't really relative to anything. Rectified Airspeed (RAS) or Calibrated Air Speed (CAS) This is IAS corrected for ...


22

An (analog) machmeter looks something like this: So it's more like an more complex version of the airspeed indicator, in this case correcting for the altitude in the process. That being said, I found this extract apparently from an FAA publication: Some older mechanical Machmeters not driven from an air data computer use an altitude aneroid inside the ...


22

There are three different speeds that are of relevance here: Groundspeed- This is probably the speed indicated to the passenger. For them, this is the most relevant as it determines the time taken for the trip Airspeed- This is the speed of relevance to the flight crew and is used for flight. Local airspeed- This determines the maximum speed of (subsonic) ...


22

Yes you must slow down to the white arc, or whatever your flap extension speed is for a given condition, regardless. If you are 10kts above the white arc and drop flaps anyway, it's not going to make the airplane come apart, and if you did it once, slap yourself on the wrist and don't do it again. It's putting stress on the flap attachments beyond what ...


21

Most modern jets use an Air Data Computer (ADC) to calculate (among other things) Mach Number. Air Data Computer An ADC is simply a computer which accepts measurements of atmospheric data to calculate various flight related data. A typical ADC may be connected to$^1$: Inputs Static System Pressure Pitot Pressure Total Air Temperature (TAT) Outputs (...


21

Information displayed to passengers through the entertainment system often gives the aircraft ground speed rather than airspeed. Wind affects the ground speed, you're right about that. Few things out of the way first. Pilots do not use ground speed for flying, instead they use indicated airspeed. Mach number is not derived from the ground speed, as it is ...


21

Aircraft are limited by both air speed (VMO, affects loads on the structures) and Mach (MMO, formation of shock waves resulting in buffet). At low altitudes, the speed of sound is high so an aircraft is most limited by indicated airspeed (IAS). At higher altitudes, the speed of sound is lower so the aircraft will be limited by Mach number. Aircraft ...


21

now, if you're looking at modern, more commonly used transportation, powered paragliding would probably take the cake. CC BY 3.0, https://en.wikipedia.org/w/index.php?curid=13110495 Powered paragliders usually fly between 15 and 50 mph (25 and 72 km/h) at altitudes from 'foot-dragging on the water' up to 24,000+ ft (5400 m) https://en.wikipedia.org/...


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